This recipe creates custom fields for membership registration and has a custom profile field function that may be used to display a Register Helper field only to membership manager or administrators.

my-pmprorh-manager-and-adminstrator-only-fields.php

<?php
/**
 * This recipe creates custom fields for membership registration and
 * has a custom profile field function that may be used to display a field
 * only to membership manager or administrators.
 *
 * @requires Register Helper Add On
 * @link https://www.paidmembershipspro.com/add-ons/pmpro-register-helper-add-checkout-and-profile-fields/
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmprorh_init_example_display_field_for_admin_and_membership_manager_only() {
	// don't break if Register Helper is not loaded
	if ( ! function_exists( 'pmprorh_add_registration_field' ) ) {
		return false;
	}

	$admin_and_membership_manager = 'only_admin';
	if ( is_user_logged_in() && current_user_can( 'pmpro_membership_manager' ) ) {
		$admin_and_membership_manager = true;
	}

	// define the fields
		$fields = array();
	// TEXT FIELD - Basic Example
	$fields[] = new PMProRH_Field(
		'basic_example', // input field name, used as meta key
		'text',          // field type
		array(
			'label'    => 'Basic Example', // field label
			'profile'  => true,            // display on user profile
			'required' => true,           // optional field
		)
	);

	$fields[] = new PMProRH_Field(
		'admin_and_membership_manager_example', // input field name, used as meta key
		'text',          // field type
		array(
			'label'    => 'Admin and Manager Only', // field label
			'profile'  => $admin_and_membership_manager, // display on user profile if admin or membership manager
			'required' => true,           // optional field
		)
	);
	$fields[] = new PMProRH_Field(
		'only_admin_example', // input field name, used as meta key
		'text',          // field type
		array(
			'label'    => 'Admin Only', // field label
			'profile'  => 'only_admin',            // display on user profile
			'required' => true,           // optional field
		)
	);

	foreach ( $fields as $field ) {
		pmprorh_add_registration_field(
			'checkout_boxes', // location on checkout page
			$field            // PMProRH_Field object
		);
	}
	// that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action( 'init', 'my_pmprorh_init_example_display_field_for_admin_and_membership_manager_only' );

Thunsis, I can see how this works, but can I check on something (code golf)?

If I just wanted to have a set of RH fields that were displayed only to the Administrator and Membership Manager roles, could I simply wrap the RH field setup in a current_user_can() conditional? Logically, something like this:

function my_pmprorh_admin_init(){

	if ( is_user_logged_in() && is_admin() || current_user_can ( 'manage_options' ) || current_user_can ( 'pmpro_membership_manager') ) {

		$fields   = array();

		$fields[] = new PMProRH_Field(
			'user_notes',
			'textarea',
			array(
				'label'          => 'User Notes',
				'rows'           => 5,
				'cols'           => 50,
				'profile'        => true,
				'memberslistcsv' => true,
				)
			);

		foreach ( $fields as $field ) {
			pmprorh_add_registration_field(
				'checkout_boxes',
				$field
			);
		}
	}
}
add_action( 'init', 'my_pmprorh_admin_init' );

Whatever fields are put inside this conditional would only be setup if the logged in user was an Administrator or Membership Manager, right?

I appreciate that your code gist can be used within a 'standard' RH setup i.e. 'all-in-one', but I already have many different RH setups so that I can position them within different sections of the checkout page.

Ahhh, the || operator would return true therefore the if statement would ignore whether the user was logged in or whether the page request was an admin page. Two conditionals?

if ( is_user_logged_in() && is_admin() ) {
	if ( current_user_can ( 'manage_options' ) || current_user_can ( 'pmpro_membership_manager' ) ) {

	<RH Fields Setup>
	
	}
}